An optical system of the type mentioned above is known from EP 0 851 304 A.
Without any restriction of the generality, the optical system mentioned above will be described for a projection objective for microlithography, but without the present invention being restricted to this.
A projection objective is a part of a projection exposure installation that is used to produce semiconductor components. For this purpose, a pattern which is arranged on an object plane of the projection objective and is referred to as a reticle is imaged by means of the projection objective onto a photosensitive layer on a substrate, which is referred to as a wafer.
As a result of the continuous progress in miniaturization of the structures of the semiconductor components to be produced, the imaging characteristics of projection objectives are subject to increasingly more stringent requirements.
There is therefore always an aim to reduce imaging errors of projection objectives for microlithography to a very low level. While production-dependent imaging errors in the case of a projection objective can already be corrected after the production of the projection objective by reworking, for example by making individual lenses or mirrors of the projection objective aspherical, it is more difficult to correct imaging errors which occur during operation.
During operation, the imaging light which is used is partially absorbed by the optical elements of the projection objective, which leads to heating of the optical elements of the projection objective. The heating induces imaging errors which can assume complicated field profiles, particularly when, as is the case in modern projection exposure installations, the beam path through the projection objective is not rotationally symmetrical with respect to the optical axis, and, in particular, only a subarea of individual optical elements is used by the beam path. Furthermore, specific types of illumination (also referred to as illumination settings) are increasingly being used in modern projection exposure installations, in particular dipole or quadrupole illuminations. These multipole illuminations lead in particular to higher-order imaging errors, and/or imaging errors in higher Zernike orders.
The document EP 0 851 304 A, which has been cited above, describes an optical system in the form of a projection, objective for microlithography, which has an optical correction arrangement in order to compensate for heat-induced imaging errors which occur during operation. A first exemplary embodiment of the optical correction arrangement has two optical correction elements, which both each have an aspherical surface contour on their mutually facing surfaces, wherein the two aspherical surface contours of the two correction elements add up to at least approximately zero. A correction arrangement such as this is also referred to as an Alvarez manipulator.
In an initial position (null position) of the two correction elements, the optical effects of the aspherical surface contours of the two correction elements cancel, one another out. In this known correction arrangement, the two correction elements can be moved with respect to the optical axis, translationally, transversely relative to one another. The translational movement of the correction elements relative to one another shifts the aspherical surface contours of the two correction elements with respect to one another, thus achieving a resultant optical effect on the wavefront passing through the two correction elements. This optical effect is then used for correction of an imaging error, wherein the aspherical surface contours are for this purpose matched to the imaging error to be compensated for.
The same document also describes an Alvarez manipulator which is formed from a total of three correction elements, wherein the first correction element together with the second correction element forms a first correction element pair, and the second correction element together with the third correction element forms a second correction element pair.
The document JP 10-142555 A discloses a projection objective for microlithography which has an optical correction arrangement for correction of distortion. The correction arrangement has at least two optical correction elements, whose mutually opposite surfaces have contours which are complementary to one another. The two correction elements are shifted relative to one another in the direction of the optical axis, in order to correct distortion.
While carrying out a lithographical production method for production of semiconductor components, it is sometimes necessary to rotate the illumination setting around the optical axis in order to allow both horizontally aligned and vertically aligned structures to be manufactured, with an optimum illumination setting. Furthermore, in some cases, it is also necessary to use the projection objective to image structures which are arranged in arbitrary angular orientations. The variation of the illumination setting once again results in new imaging errors, which cannot be compensated for sufficiently quickly in known optical systems. In other words, the known optical systems are not suitable for reacting sufficiently quickly to different illumination settings and, in fact, these optical systems require the removal of the optical correction arrangement, and the installation of a correction arrangement which is appropriately matched to the new illumination setting.
The document EP 0 660 169 A describes a projection exposure installation in which an optical correction arrangement is provided for correction of non-rotationally symmetrical imaging errors. The optical correction arrangement in this known optical system has two cylindrical lenses, one of which has a negative refractive power, while the other has a positive refractive power. When the two cylindrical lenses are arranged such that their cylinder axes run parallel to one another, the two cylindrical lenses together produce no optical effect, provided that the absolute values of the refractive powers are of equal magnitude. If the two cylindrical lenses are rotated relative to one another such that their cylindrical axes are at right angles to one another, this maximizes their optical, in this case astigmatic, effect. However, the use of cylindrical lenses as correction elements restricts the flexibility and the number of imaging errors which can be corrected and, in particular, allows only low-order imaging errors to be corrected.